Adjustable click-type torque wrenches have been commercially produced and have been in wide use since the 1950s. The great majority of adjustable click-type torque wrenches provided by the prior art are characterized by elongate tubular lever arms with open front and front ends. Tool (drive socket) engaging heads are pivotally carried at the front ends of the lever arms. The heads carry elongate pivot arms that project rearwardly and freely within the front end portions of the lever arms. The rear ends of the pivot arms are formed with or carry flat rearwardly disclosed front trip block seats. Within the arms and spaced rearward from the front seats are axially movable plungers with flat forwardly disposed trip block rear seats. Trip blocks with flat front and rear faces are positioned between the front and rear trip block seats with their front and rear faces normally occurring in flat seated engagement therewith. Elongate helical compression springs are positioned in the rear end portions of the lever arms and engage and yieldingly urge the plungers forwardly and thereby hold the trip blocks in seated engagement with and between the front and rear seats. The trip blocks normally hold the pivot arms concentric or centrally within the lever arms and spaced radially inward from the inside surfaces of the lever arms. Torsional forces directed onto and through the head of these wrenches cause the pivot arms to pivot. When the torsional forces are sufficient to overcome the forces of the springs acting upon the plungers, the trip blocks are caused to turn or tip out of seated engagement with the seats; urging the plungers rearwardly against the resistance of the springs; and, causing the rear ends of the pivot arms to swing radially within the lever arms and to strike the interior surfaces of the lever arms, creating an audible sound or "click." By selectively varying the extent to which the springs are biased and the forces at which the plungers are urged forwardly, the torsional or forces at which the wrenches actuate to generate their "click" can be accurately adjusted.
To the above end, wrenches of the class here concerned with are provided with adjusting means to effect accurate adjustment of the springs. Typically, the adjusting means include screw mechanisms at the rear end portions of the lever arms. The adjusting means are selectively manually operable to increase and decrease the extent to which the springs are axially biased. The adjusting means further include scales related to the screw mechanisms and the lever arms that indicate the axial position of the rear ends of springs and the extent to which the springs are biased and that translate the positions of the springs into units of force. Further, the adjusting means include calibrating means that enable the positioning of the parts of the adjusting means to be moved and set to properly correlate the positioning of the springs with the scales.
To the best of my knowledge and belief, all of the adjusting means for adjustable click-type wrenches that the prior art provides include at least one and often several extremely costly-to-make machined parts. As a result of the foregoing, adjustable click-type torque wrenches of the character here concerned with and that meet those long-established minimum standards for such tools are costly tools.
Throughout the 1980s, the great majority of adjustable click-type torque wrenches that met the requirements of industry and proved to be commercially successful were patented wrenches produced by several European and United States torque tool manufacturers. Since the mid-1980s, the patents held by the manufacturers of torque wrenches have expired and the special know-how that must be exercised to effectively produce those tools has been acquired by tool manufacturers In several Asian countries including Korea, Taiwan and China. As a result of the foregoing, and because the cost of both material and labor are notably less in those Asian countries than in the United States and in Europe, an ever-increasing number of torque wrenches manufactured in the above-noted Asian countries are appearing in the United States marketplace. Those foreign-made wrenches are identical to those wrenches that have long been made by European and United States tool manufacturers, and their retail prices are well below the cost of manufacture of the identical tools in the United States. As a result of the foregoing, the manufacture of torque wrenches in the United States is becoming unprofitable and the United States manufacturers of such wrenches have or are being forced to discontinue the manufacture of such tools in the United States. As a result of the foregoing, some domestic manufacturers of such tools have gone out of business. Others, with valuable trademarks, goodwill and reputation that will sustain a profitable tool distribution and marketing program have turned to purchasing inexpensive, foreign-made, adjustable click-type torque wrenches and are distributing and selling them as their own manufactured goods,